1. Field of the Invention
This invention relates to a centrifugal pump impeller and particularly to an impeller that can prevent turbulence at the inlet of the pump for improving pumping efficiency and enables accurate positioning of the vane for the impeller.
2. Description of the Prior Art
In the design and fabrication of impeller for centrifugal pump, how to improve pumping efficiency of the vane and to make positioning of the vane simple in the assembly are some of the heavily focused issues. The surface smoothness at the inlet of the impeller may directly affect flow streamline in the passage and pumping efficiency. To avoid forming abrupt surface change at the impeller inlet is one of the key design consideration. As an impeller usually has at least six blades and each blade is formed in an irregular spiral shape, to accurately position the blades for assembling the vane is not easy. When the blades are not accurately-positioned, the pumping efficiency will be negatively impacted.
Furthermore conventional rear vane cover plate of the pump usually is made by pressing. The cover plate has relatively large size and may result in lower structural strength. It also tends to form corrugation (with rough surface). This phenomenon happens most often to an impeller (or pump) with smaller specific speed. Conventional technique uses increased vane cover plate thickness to enhance strength and employs high cost machining work to further improve cover plate precision. It increases cost and drags down fabrication efficiency.
Some improvement techniques have been announced to address these issues. U.S. Pat. No. 5,082,425 discloses a technique that forms a plurality of corrugation structure on the vane cover plate mating with the vane base to facilitate the blade positioning in the impeller. The corrugation structure needs elaborated design and high precision machining, and also needs accurate soldering work to put the blades in place. The design and fabrication are expensive. Moreover the vanes at the inlet side still cannot totally align with the front end of the hub and suction port. As a result, a not smooth surface will be formed for the vane around the hub and suction port at the inlet area. Flowing fluid easily produces turbulence at this area and greatly impact pumping efficiency.
German Pat. No. DE 44 46 193 C2 discloses another impeller structure that has a plurality of thin spiral vanes soldering to the front and rear vane cover plate by means of laser soldering operation. It may improve surface smoothness of the vane at the inlet and reduce turbulence. However laser soldering operation costs higher, and the blade positioning problem remains unresolved.